Visual Prosthesis

ABSTRACT

A visual prosthesis apparatus and a method for limiting power consumption in a visual prosthesis apparatus. The visual prosthesis apparatus comprises a camera for capturing a video image, a video processing unit associated with the camera, the video processing unit configured to convert the video image to stimulation patterns, and a retinal stimulation system configured to stop stimulating neural tissue in a subject&#39;s eye based on the stimulation patterns when an error is detected in a forward telemetry received from the video processing unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application, and claim priority to U.S.application Ser. No. 11/874,690, filed Oct. 18, 2007, for VisualProsthesis, which claims the benefit of U.S. provisional PatentApplication Ser. No. 60/852,875, filed Oct. 19, 2006 for “Data TelemetrySecurity for an Implantable Device” by Robert J. Greenberg, Kelly H.McClure and Arup Roy, the disclosure of which is incorporated herein byreference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The present invention was made with support from the United StatesGovernment under Grant number R24EY12893-01, awarded by the NationalInstitutes of Health. The United States Government has certain rights inthe invention.

FIELD

The present disclosure relates to visual prostheses configured toprovide neutral stimulation for the creation of artificial vision.

BACKGROUND

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andpositions of phosphenes; (2) that increase stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparatuses to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular visual prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases such as retinitis pigmentosaand age related macular degeneration which affect millions of peopleworldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the information as a sequence of electricalpulses which are relayed to the nervous system via the prostheticdevice. In this way, it is possible to provide artificial sensationsincluding vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretial). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, and avoid undue compression of thevisual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Opthalmol. 272 (1985). These retinaltacks have proved to be biocompatible and remain embedded in the retina,and choroid/sclera, effectively pinning the retina against the choroidand the posterior aspects of the globe. Retinal tacks are one way toattach a retinal array to the retina. U.S. Pat. No. 5,109,844 to de Juandescribes a flat electrode array placed against the retina for visualstimulation. U.S. Pat. No. 5,935,155 to Humayun describes a visualprosthesis for use with the flat retinal array described in de Juan.

SUMMARY

According to a first aspect, a visual prosthesis apparatus is disclosed,the a visual prosthesis apparatus comprising: a camera for capturing avideo image; a video processing unit associated with the camera, thevideo processing unit configured to convert the video image tostimulation patterns; and a retinal stimulation system configured tostop stimulating neural tissue in a subject's eye based on thestimulation patterns when an error is detected in a forward telemetryreceived from the video processing unit.

According to a second aspect, method for limiting power consumption in avisual prosthesis apparatus comprising a video capture device and aretinal stimulation system is disclosed, the method comprising:determining if a subject is wearing the video capture device; andtransmitting power and data to the retinal stimulation system only aslong as the subject is wearing the video capture device.

According to a third aspect, a method for limiting power consumption ina visual prosthesis apparatus comprising a retinal stimulation systemand a video processing unit is disclosed, the method comprising:determining if the retinal stimulation system is transmitting a backtelemetry to the video processing unit; and transmitting power and datato the retinal stimulation system only as long as the retinalstimulation system transmits the back telemetry.

According to a fourth aspect, a visual prosthesis apparatus isdisclosed, the a visual prosthesis apparatus comprising: a camera forcapturing a video image; and a video processing unit associated with thecamera and associated with a retinal stimulation system, wherein thevideo processing unit is configured to convert the video image tostimulation patterns and transmit the stimulation patterns to theretinal stimulation system for stimulation of neural tissue in asubject's eye, and the video processing unit is configured to stoptransmitting the stimulation patterns to the retinal stimulation systemwhen the retinal stimulation system does not transmit back telemetry orwhen the retinal stimulation system detects an error in a forwardtelemetry received from the video processing unit.

According to a fifth aspect, a method for limiting power consumption ina visual prosthesis apparatus comprising a retinal stimulation systemand a video processing unit is disclosed, the method comprising: a)transmitting power and data via forward telemetry to the retinalstimulation system; b) determining if the retinal stimulation system istransmitting a back telemetry to the video processing unit; c) stoptransmitting the power and the data via forward telemetry to the retinalstimulation system when the retinal stimulation system does not transmitthe back telemetry; d) transmitting the power to the retinal stimulationsystem for a predetermined amount of time; e) determining if the retinalstimulation system is transmitting the back telemetry during thepredetermined amount of time; f) stop transmitting power to the retinalstimulation system when the retinal stimulation system does not transmitthe back telemetry during the predetermined amount of time; and g)repeating features d) through D until the retinal stimulation systemtransmits the back telemetry.

Further embodiments are shown in the specification, drawings and claimsof the present application.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a visual prosthesis apparatus according to the presentdisclosure.

FIGS. 2 and 3 show a retinal stimulation system adapted to be implantedinto a subject.

FIG. 4 shows a front view of the implanted retinal stimulation system.

FIG. 5 shows a side view of the implanted system of FIG. 9.

FIGS. 6 and 7 show a video capture/transmission apparatus or visoradapted to be used in combination with the retinal stimulation of FIGS.2 and 3.

FIG. 8 shows a flexible circuit electrode array, also shown in FIG. 2.

FIG. 9 shows components of a fitting system according to the presentdisclosure, the system also comprising the visor shown in FIGS. 4 and 5.

FIG. 10 shows the visual prosthesis apparatus in a stand-alone mode,i.e. comprising the visor connected to a video processing unit.

FIGS. 11-12 show the video processing unit already briefly shown withreference to FIG. 8.

FIG. 13 a shows a LOSS OF SYNC mode.

FIG. 13 b shows an exemplary block diagram of the steps taken when VPUdoes not receive back telemetry from the Retinal stimulation system.

FIG. 13 c shows an exemplary block diagram of the steps taken when thesubject is not wearing Glasses.

FIGS. 14-1, 14-2, 14-3 and 14-4 show an exemplary embodiment of a videoprocessing unit. FIG. 14-1 should be viewed at the left of FIG. 14-2.FIG. 14-3 should be viewed at the left of FIG. 14-4. FIGS. 14-1 and 14-2should be viewed on top of FIGS. 14-3 and 14-4.

In the following description, like reference numbers are used toidentify like elements. Furthermore, the drawings are intended toillustrate major features of exemplary embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of everyimplementation nor relative dimensions of the depicted elements, and arenot drawn to scale.

DETAILED DESCRIPTION

The present disclosure is concerned with a visual apparatus and a methodfor creation of artificial vision. In particular, the present disclosureprovides an interface and method for controlling a visual prosthesis(i.e. device) implanted in an individual patient (i.e. subject) tocreate artificial vision.

FIG. 1 shows a visual prosthesis apparatus. The visual apparatuscomprises, in combination, an implantable retinal stimulation system 1and a video capture/transmission apparatus or visor embodied invisor/Glasses 5. An exemplary retinal stimulation system 1 is shown inmore detail in FIGS. 2 and 3 and an exemplary visor 5 is shown in moredetail in FIGS. 6 and 7.

The retinal stimulation system 1 is further disclosed in U.S.application Ser. No. 11/207,644, filed Aug. 19, 2005 for “FlexibleCircuit Electrode Array” by Robert J. Greenberg, et, al. incorporatedherein by reference, and is intended for use in subjects with retinitispigmentosa. The visor 5 is further disclosed in International PatentApplication No. PCT/US07/13918, (Applicant's Docket No. S416-PCT) filedon Jun. 14, 2007 and entitled “APPARATUS AND METHOD FOR ELECTRICALSTIMULATION OF HUMAN RETINA,” also incorporated herein by reference.

The exemplary retinal stimulation system 1, shown in FIGS. 2 and 3, isan implantable electronic device containing an inductive coil 116 and anelectrode array 2 that is electrically coupled by a cable 3 that piercessclera of the subject's eye to an electronics package 4, external to thesclera. The retinal stimulation system 1 is designed, for example, toelicit visual percepts in blind subjects with retinitis pigmentosa.

Human vision provides a field of view that is wider than it is high.This is partially due to fact that we have two eyes, but even a singleeye provides a field of view that is approximately 90° high and 140° to160° degrees wide. It is therefore, advantageous to provide a flexiblecircuit electrode array 2 that is wider than it is tall. This is equallyapplicable to a cortical visual array. In which case, the widerdimension is not horizontal on the visual cortex, but corresponds tohorizontal in the visual scene.

FIG. 8 shows the flexible circuit electrode array 2 prior to folding andattaching to the electronics package 4 of FIG. 2. At one end of theflexible circuit cable 3 is an interconnection pad 52 for connection tothe electronics package 4. At the other end of the flexible circuitcable 3 is the flexible circuit electrode array 2. Further, anattachment point 54 may be provided near the flexible circuit electrodearray 2. A retina tack (not shown) is placed through the attachmentpoint 54 to hold the flexible circuit electrode array 2 to the retina. Astress relief 57 may be provided surrounding the attachment point 54.The stress relief 57 may be made of a softer polymer than the flexiblecircuit, or it may include cutouts or thinning of the polymer to reducethe stress transmitted from the retina tack to the flexible circuitelectrode array 2. The flexible circuit cable 3 may be formed in a dogleg pattern so than when it is folded at fold 48 it effectively forms astraight flexible circuit cable 3 with a narrower portion at the fold 48for passing through the sclerotomy. The electrode array 2 may comprise apolyimide cable that houses wire conductors and an array of exposedplatinum electrodes in a grid. In one embodiment, there are sixtyelectrodes arranged in a 6×10 grid.

The electronics package 4 of FIGS. 2 and 3 can be electrically coupledto the inductive coil 116. In one aspect, the inductive coil 116contains a receiver and transmitter antennae made from wound wire.Alternatively, the inductive coil 116 may be made from a thin filmpolymer sandwich with wire traces deposited between layers of thin filmpolymer. The electronics package 4 may contain components and anApplication Specific Integrated Circuit (ASIC) for processing thereceived data and using the received power to generate the requiredstimulation output. The electronics package 4 and the inductive coil 116may be held together by a molded body 118 shown in FIG. 3. As also shownin FIG. 3, the molded body 118 may also include suture tabs 120 shown inFIG. 3. The molded body narrows to form a strap 122 which surrounds thesclera and holds the molded body 118, inductive coil 116, andelectronics package 4 in place. The molded body 118, suture tabs 120 andstrap 122 are preferably an integrated unit made of silicone elastomer.Silicone elastomer can be formed in a pre-curved shape to match thecurvature of a typical sclera. Furthermore, silicone remains flexibleenough to accommodate implantation and to adapt to variations in thecurvature of an individual sclera. In one aspect, the inductive coil 116and molded body 118 are oval shaped, and in this way, a strap 122 canbetter support the oval shaped coil.

The eye moves constantly. The eye moves to scan a scene and also has ajitter motion to prevent image stabilization. Even though such motion isuseless in the blind, it often continues long after a person has losttheir sight. Thus, in one embodiment of the present disclosure, theentire retinal stimulation system 1 of the prosthesis is attached to andsupported by the sclera of a subject. By placing the device under therectus muscles with the electronics package in an area of fatty tissuebetween the rectus muscles, eye motion does not cause any flexing whichmight fatigue, and eventually damage, the device.

FIG. 3 shows a side view of the retinal stimulation system 1, inparticular, emphasizing the fan tail 124. When the retinal prosthesis isimplanted, the strap 122 is passed under the eye muscles to surround thesclera. The inductive coil 116 and molded body 118 should also followthe strap under the lateral rectus muscle on the side of the sclera. Theretinal stimulation system 1 of the visual prosthesis apparatus is verydelicate. It is easy to tear the molded body 118 or break wires in theinductive coil 116. In order to allow the molded body 118 to slidesmoothly under the lateral rectus muscle, the molded body is shaped inthe form of a fan tail 124 on the end opposite the electronics package4. Element 123 shows a retention sleeve, while elements 126 and 128 showholes for surgical positioning and a ramp for surgical positioning,respectively.

FIGS. 4 and 5 show front and side views of the Retinal stimulationsystem 1 implanted with respect to the subject's eye 7. As shown inFIGS. 4 and 5, the electrode array 2 enters the eye through a pars planaincision and is placed on the retina over the fovea using a retinaltack. The remaining Retinal stimulation system 1 is secured to the eyeby means of a scleral band held in place by a Watzke sleeve (typical ofscleral procedures), and also by suture tabs. Additionally, anothersuture may be placed around the scleral band in the inferior medicalquadrant of the eye.

Referring to FIGS. 6 and 7, the glasses 5 may comprise, for example, aframe 11 holding a camera 12, an external coil 14 and a mounting system16 for the external coil 14. The mounting system 16 may also enclose theRF circuitry. In this configuration, the video camera 12 captures livevideo. The video signal is sent to an external Video Processing Unit(VPU) 20 (shown in FIGS. 9, 11 and 12 and discussed below), whichprocesses the video signal and subsequently transforms the processedvideo signal into electrical stimulation patterns or data. Theelectrical stimulation data are then sent to the external coil 14 thatsends both data and power via radio-frequency (RF) telemetry to the coil116 of the retinal stimulation system 1, shown in FIGS. 2 and 3. Thecoil 116 receives the RF commands which control the application specificintegrated circuit (ASIC) which in turn delivers stimulation to theretina of the subject via a thin film electrode array (TFEA). In oneaspect of an embodiment, light amplitude is recorded by the camera 12.The VPU 20 may use a logarithmic encoding scheme to convert the incominglight amplitudes into the electrical stimulation patterns or data. Theseelectrical stimulation patterns or data may then be passed on to theRetinal Stimulation System 1, which results in the retinal cells beingstimulated via the electrodes in the electrode array 2 (shown in FIGS.2, 3 and 8). In one exemplary embodiment, the electrical stimulationpatterns or data being transmitted by the external coil 14 is binarydata. The external coil 14 may contain a receiver and transmitterantennae and a radio-frequency (RF) electronics card for communicatingwith the internal coil 116.

Referring to FIG. 9, a Fitting System (FS) may be used to configure andoptimize the visual prosthesis apparatus shown in FIG. 1. The FittingSystem is fully described in the related application U.S. applicationSer. No. 11/796,425, filed on Apr. 27, 2007, (Applicant's Docket No.S401-USA) which is incorporated herein by reference in its entirety.

The Fitting System may comprise custom software with a graphical userinterface running on a dedicated laptop computer 10. Within the FittingSystem are modules for performing diagnostic checks of the implant,loading and executing video configuration files, viewing electrodevoltage waveforms, and aiding in conducting psychophysical experiments.A video module can be used to download a video configuration file to theVideo Processing Unit (VPU) 20 discussed above and store it innon-volatile memory to control various aspects of video configuration,e.g. the spatial relationship between the video input and theelectrodes. The software can also load a previously used videoconfiguration file from the VPU 20 for adjustment.

The Fitting System can be connected to the Psychophysical Test System(PTS), located for example on a dedicated laptop 30, in order to runpsychophysical experiments. In psychophysics mode, the Fitting Systemenables individual electrode control, permitting clinicians to constructtest stimuli with control over current amplitude, pulse-width, andfrequency of the stimulation. In addition, the psychophysics moduleallows the clinician to record subject responses. The PTS may include acollection of standard psychophysics experiments developed using forexample MATLAB (MathWorks) software and other tools to allow theclinicians to develop customized psychophysics experiment scripts.

Using the psychophysics module, important perceptual parameters such asperceptual threshold, maximum comfort level, and spatial location ofpercepts may be reliably measured. Based on these perceptual parameters,the fitting software enables custom configuration of the transformationbetween video image and spatio-temporal electrode stimulation parametersin an effort to optimize the effectiveness of the retinal prosthesis foreach subject.

The Fitting System laptop 10 of FIG. 9 may be connected to the VPU 20using an optically isolated serial connection adapter 40. Because it isoptically isolated, the serial connection adapter 40 assures that noelectric leakage current can flow from the Fitting System laptop 10 inthe even of a fault condition.

As shown in FIG. 9, the following components may be used with theFitting System according to the present disclosure. The Video ProcessingUnit (VPU) 20 for the subject being tested, a Charged Battery 25 for VPU20, the Glasses 5, a Fitting System (FS) Laptop 10, a PsychophysicalTest System (PTS) Laptop 30, a PTS CD (not shown), a CommunicationAdapter (CA) 40, a USB Drive (Security) (not shown), a USB Drive(Transfer) 47, a USB Drive (Video Settings) (not shown), a Patient InputDevice (RF Tablet) 50, a further Patient Input Device (Jog Dial) 55,Glasses Cable 15, CA-VPU Cable 70, FS-CA Cable 45, FS-PTS Cable 46, Four(4) Port USB Hub 47, Mouse 60, Test Array system 80, Archival USB Drive49, an Isolation Transformer (not shown), adapter cables (not shown),and an External Monitor (not shown).

With continued reference to FIG. 9, the external components of theFitting System may be configured as follows. The battery 25 is connectedwith the VPU 20. The PTS Laptop 30 is connected to FS Laptop 10 usingthe FS-PTS Cable 46. The PTS Laptop 30 and FS Laptop 10 are plugged intothe Isolation Transformer (not shown) using the Adapter Cables (notshown). The Isolation Transformer is plugged into the wall outlet. Thefour (4) Port USB Hub 47 is connected to the FS laptop 10 at the USBport. The mouse 60 and the two Patient Input Devices 50 and 55 areconnected to four (4) Port USB Hubs 47. The FS laptop 10 is connected tothe Communication Adapter (CA) 40 using the FS-CA Cable 45. The CA 40 isconnected to the VPU 20 using the CA-VPU Cable 70. The Glasses 5 areconnected to the VPU 20 using the Glasses Cable 15.

In one exemplary embodiment, the Fitting System shown in FIG. 9 may beused to configure system stimulation parameters and video processingstrategies for each subject outfitted with the visual prosthesisapparatus of FIG. 1. The fitting application, operating system, laptops10 and 30, isolation unit and VPU 20 may be tested and configurationcontrolled as a system. The software provides modules for electrodecontrol, allowing an interactive construction of test stimuli withcontrol over amplitude, pulse width, and frequency of the stimulationwaveform of each electrode in the Retinal stimulation system 1. Theseparameters are checked to ensure that maximum charge per phase limits,charge balance, and power limitations are met before the test stimuliare presented to the subject. Additionally, these parameters may bechecked a second time by the VPU 20's firmware. The Fitting System shownin FIG. 9 may also provide a psychophysics module for administering aseries of previously determined test stimuli to record subject'sresponses. These responses may be indicated by a keypad 50 and orverbally. The psychophysics module may also be used to reliably measureperceptual parameters such as perceptual threshold, maximum comfortlevel, and spatial location of percepts. These perceptual parameters maybe used to custom configure the transformation between the video imageand spatio-tempral electrode stimulation parameters thereby optimizingthe effectiveness of the visual prosthesis for each subject. The FittingSystem is fully described in the related application U.S. applicationSer. No. 11/796,425, filed on Apr. 27, 2007, (Applicant's Docket No.S401-USA) which is incorporated herein by reference in its entirety.

The visual prosthesis apparatus of FIG. 1 may operate in two modes: i)stand-alone mode and ii) communication mode

Stand-Alone Mode

Referring to FIGS. 1, 2 and 10, in the stand-alone mode, the videocamera 12, on the glasses 5, captures a video image that is sent to theVPU 20. The VPU 20 processes the image from the camera 12 and transformsit into electrical stimulation patterns that are transmitted to theexternal coil 14. The external coil 14 sends the electrical stimulationpatterns and power via radio-frequency (RF) telemetry to the implantedretinal stimulation system 1 (FIGS. 2 and 3). The internal coil 116 ofthe retinal stimulation system 1 receives the RF commands from theexternal coil 14 and transmits them to the electronics package 4 that inturn delivers stimulation to the retina via the electrode array 2.Additionally, the retinal stimulation system 1 may communicate safetyand operational status back to the VPU 20 by transmitting RF telemetryfrom the internal coil 116 to the external coil 14. The visualprosthesis apparatus of FIG. 1 may be configured to electricallyactivate the retinal stimulation system 1 only when it is powered by theVPU 20 through the external coil 14. The stand-alone mode may be usedfor clinical testing and/or at-home use by the subject

Communication Mode

The communication mode may be used for diagnostic testing,psychophysical testing, patient fitting and downloading of stimulationsettings to the VPU 20 before transmitting data from the VPU 20 to theretinal stimulation system 1 as is done for example in the stand-alonemode described above. Referring to FIG. 9, in the communication mode,the VPU 20 is connected to the Fitting System laptop 10 using cables 70,45 and the optically isolated serial connection adapter 40. In thismode, laptop 10 generated stimuli may be presented to the subject andprogramming parameters may be adjusted and downloaded to the VPU 20. ThePsychophysical Test System (PTS) laptop 30 connected to the FittingSystem laptop 10 may also be utilized to perform more sophisticatedtesting and analysis as fully described in the related application U.S.application Ser. No. 11/796,425, filed on Apr. 27, 2007, (Applicant'sDocket No. S401-USA) which is incorporated herein by reference in itsentirety.

In one embodiment, the functionality of the retinal stimulation system 1can also be tested pre-operatively and intra-operatively (i.e. beforeoperation and during operation) by using an external coil 14, withoutthe glasses 5, placed in close proximity to the retinal stimulationsystem 1. The coil 14 may communicate the status of the retinalstimulation system 1 to the VPU 20 that is connected to the FittingSystem laptop 10 as shown in FIG. 9.

As discussed above, the VPU 20 processes the image from the camera 12and transforms the image into electrical stimulation patterns for theretinal stimulation system 1. Filters such as edge detection filters maybe applied to the electrical stimulation patterns for example by the VPU20 to generate, for example, a stimulation pattern based on filteredvideo data that the VPU 20 turns into stimulation data for the retinalstimulation system 1. The images may then be reduced in resolution usinga downscaling filter. In one exemplary embodiment, the resolution of theimage may be reduced to match the number of electrodes in the electrodearray 2 of the retinal stimulation system 1. That is, if the electrodearray has, for example, sixty electrodes, the image may be reduced to asixty channel resolution. After the reduction in resolution, the imageis mapped to stimulation intensity using for example a look-up tablethat has been derived from testing of individual subjects. Then, the VPU20 transmits the stimulation parameters via forward telemetry to theretinal stimulation system 1 in frames that may employ a cyclicredundancy check (CRC) error detection scheme.

In one exemplary embodiment, the VPU 20 may be configured to allow thesubject/patient i) to turn the visual prosthesis apparatus on and off,ii) to manually adjust settings, and iii) to provide power and data tothe retinal stimulation system 1. Referring to FIGS. 11 and 12, the VPU20 may comprise a case 800, power button 805 for turning the VPU 20 onand off, setting button 810, zoom buttons 820 for controlling the camera12, connector port 815 for connecting to the Glasses 5, a connector port816 for connecting to the laptop 10 through the connection adapter 40,indicator lights 825 to give visual indication of operating status ofthe system, the rechargeable battery 25 for powering the VPU 20, batterylatch 830 for locking the battery 25 in the case 800, digital circuitboards (not shown), and a speaker (not shown) to provide audible alertsto indicate various operational conditions of the system. Because theVPU 20 is used and operated by a person with minimal or no vision, thebuttons on the VPU 20 may be differently shaped and/or have specialmarkings as shown in FIG. 12 to help the user identify the functionalityof the button without having to look at it. As shown in FIG. 12, thepower button 805 may be a circular shape while the settings button 820may be square shape and the zoom buttons 820 may have special raisedmarkings 830 to also identify each buttons functionality. One skilled inthe art would appreciate that other shapes and markings can be used toidentify the buttons without departing from the spirit and scope of theinvention. For example, the markings can be recessed instead of raised.

In one embodiment, the indicator lights 825 may indicate that the VPU 20is going through system start-up diagnostic testing when the one or moreindicator lights 825 are blinking fast (more then once per second) andare green in color. The indicator lights 825 may indicate that the VPU20 is operating normally when the one or more indicator lights 825 areblinking once per second and are green in color. The indicator lights825 may indicate that the retinal stimulation system 1 has a problemthat was detected by the VPU 20 at start-up diagnostic when the one ormore indicator lights 825 are blinking for example once per five secondand are green in color. The indicator lights 825 may indicate that thevideo signal from camera 12 is not being received by the VPU 20 when theone or more indicator lights 825 are always on and are amber color. Theindicator lights 825 may indicate that there is a loss of communicationbetween the retinal stimulation system 1 and the external coil 14 due tothe movement or removal of Glasses 5 while the system is operational orif the VPU 20 detects a problem with the retinal stimulation system 1and shuts off power to the retinal stimulation system 1 when the one ormore indicator lights 825 are always on and are orange color. Oneskilled in the art would appreciate that other colors and blinkingpatterns can be used to give visual indication of operating status ofthe system without departing from the spirit and scope of the invention.

In one embodiment, a single short beep from the speaker (not shown) maybe used to indicate that one of the buttons 825, 805 or 810 have beenpressed. A single beep followed by two more beeps from the speaker (notshown) may be used to indicate that VPU 20 is turned off. Two beeps fromthe speaker (not shown) may be used to indicate that VPU 20 is startingup. Three beeps from the speaker (not shown) may be used to indicatethat an error has occurred and the VPU 20 is about to shut downautomatically. As would be clear to one skilled in the are differentperiodic beeping may also be used to indicate a low battery voltagewarning, that there is a problem with the video signal, and/or there isa loss of communication between the retinal stimulation system 1 and theexternal coil 14. One skilled in the art would appreciate that othersounds can be used to give audio indication of operating status of thesystem without departing from the spirit and scope of the invention. Forexample, the beeps may be replaced by an actual prerecorded voiceindicating operating status of the system.

In one exemplary embodiment, the VPU 20 is in constant communicationwith the retinal stimulation system 1 through forward and backwardtelemetry. In this document, the forward telemetry refers totransmission from VPU 20 to the retinal stimulation system 1 and thebackward telemetry refers to transmissions from the Retinal stimulationsystem 1 to the VPU 20. During the initial setup, the VPU 20 maytransmit null frames (containing no stimulation information) until theVPU 20 synchronizes with the Retinal stimulation system 1 via the backtelemetry. In one embodiment, an audio alarm may be used to indicatewhenever the synchronization has been lost.

In order to supply power and data to the Retinal stimulation system 1,the VPU 20 may drive the external coil 14, for example, with a 3 MHzsignal. To protect the subject, the retinal stimulation system 1 maycomprise a failure detection circuit to detect direct current leakageand to notify the VPU 20 through back telemetry so that the visualprosthesis apparatus can be shut down.

The forward telemetry data (transmitted for example at 122.76 kHz) maybe modulated onto the exemplary 3 MHz carrier using Amplitude ShiftKeying (ASK), while the back telemetry data (transmitted for example at3.8 kHz) may be modulated using Frequency Shift Keying (FSK) with, forexample, 442 kHz and 457 kHz. The theoretical bit error rates can becalculated for both the ASK and FSK scheme assuming a ratio of signal tonoise (SNR). The system disclosed in the present disclosure can bereasonably expected to see bit error rates of 10-5 on forward telemetryand 10-3 on back telemetry. These errors may be caught more than 99.998%of the time by both an ASIC hardware telemetry error detection algorithmand the VPU 20's firmware. For the forward telemetry, this is due to thefact that a 16-bit cyclic redundancy check (CRC) is calculated for every1024 bits sent to the ASIC within electronics package 4 of the RetinalStimulation System 1. The ASIC of the Retinal Stimulation System 1verifies this CRC and handles corrupt data by entering a non-stimulating‘safe’ state and reporting that a telemetry error was detected to theVPU 20 via back telemetry. During the ‘safe’ mode, the VPU 20 mayattempt to return the implant to an operating state. This recovery maybe on the order of milliseconds. The back telemetry words are checkedfor a 16-bit header and a single parity bit. For further protectionagainst corrupt data being misread, the back telemetry is only checkedfor header and parity if it is recognized as properly encoded Bi-phaseMark Encoded (BPM) data. If the VPU 20 detects invalid back telemetrydata, the VPU 20 immediately changes mode to a ‘safe’ mode where theRetinal Stimulation System 1 is reset and the VPU 20 only sendsnon-stimulating data frames. Back telemetry errors cannot cause the VPU20 to do anything that would be unsafe.

The response to errors detected in data transmitted by VPU 20 may beginat the ASIC of the Retinal Stimulation System 1. The Retinal StimulationSystem 1 may be constantly checking the headers and CRCs of incomingdata frames. If either the header or CRC check fails, the ASIC of theRetinal Stimulation System 1 may enter a mode called LOSS OF SYNC 950,shown in FIG. 13 a. In LOSS OF SYNC mode 950, the Retinal StimulationSystem 1 will no longer produce a stimulation output, even if commandedto do so by the VPU 20. This cessation of stimulation occurs after theend of the stimulation frame in which the LOSS OF SYNC mode 950 isentered, thus avoiding the possibility of unbalanced pulses notcompleting stimulation. If the Retinal Stimulation System 1 remains in aLOSS OF SYNC mode 950 for 1 second or more (for example, caused bysuccessive errors in data transmitted by VPU 20), the ASIC of theRetinal Stimulation System 1 disconnects the power lines to thestimulation pulse drivers. This eliminates the possibility of anyleakage from the power supply in a prolonged LOSS OF SYNC mode 950. Fromthe LOSS OF SYNC mode 950, the Retinal Stimulation System 1 will notre-enter a stimulating mode until it has been properly initialized withvalid data transmitted by the VPU 20.

In addition, the VPU 20 may also take action when notified of the LOSSOF SYNC mode 950. As soon as the Retinal Stimulation System 1 enters theLOSS OF SYNC mode 950, the Retinal Stimulation System 1 reports thisfact to the VPU 20 through back telemetry. When the VPU 20 detects thatthe Retinal Stimulation System 1 is in LOSS OF SYNC mode 950, the VPU 20may start to send ‘safe’ data frames to the Retinal Stimulation System1. ‘Safe’ data is data in which no stimulation output is programmed andthe power to the stimulation drivers is also programmed to be off. TheVPU 20 will not send data frames to the Retinal Stimulation System 1with stimulation commands until the VPU 20 first receives back telemetryfrom the Retinal Stimulation System 1 indicating that the RetinalStimulation System 1 has exited the LOSS OF SYNC mode 950. After severalunsuccessful retries by the VPU 20 to take the implant out of LOSS OFSYNC mode 950, the VPU 20 will enter a Low Power Mode (described below)in which the implant is only powered for a very short time. In thistime, the VPU 20 checks the status of the implant. If the implantcontinues to report a LOSS OF SYNC mode 950, the VPU 20 turns power offto the Retinal Stimulation System 1 and tries again later. Since thereis no possibility of the implant electronics causing damage when it isnot powered, this mode is considered very safe.

Due to an unwanted electromagnetic interference (EMI) or electrostaticdischarge (ESD) event the VPU 20 data, specifically the VPU firmwarecode, in RAM can potentially get corrupted and may cause the VPU 20firmware to freeze. As a result, the VPU 20 firmware will stop resettingthe hardware watchdog circuit, which may cause the system to reset. Thiswill cause the watchdog timer to expire causing a system reset in, forexample, less than 2.25 seconds. Upon recovering from the reset, the VPU20 firmware logs the event and shuts itself down. VPU 20 will not allowsystem usage after this occurs once. This prevents the VPU 20 code fromfreezing for extended periods of time and hence reduces the probabilityof the VPU sending invalid data frames to the implant.

Supplying power to the Retinal stimulation system 1 can be a significantportion of the VPU 20's total power consumption. When the Retinalstimulation system 1 is not within receiving range to receive eitherpower or data from the VPU 20, the power used by the VPU 20 is wasted.

Power delivered to the Retinal stimulation system 1 may be dependant onthe orientation of the coils 14 and 116. The power delivered to theRetinal stimulation system 1 may be controlled, for example, via the VPU20 every 16.6 ms. The Retinal stimulation system 1 may report how muchpower it receives and the VPU 20 may adjust the power supply voltage ofthe RF driver to maintain a required power level on the Retinalstimulation system 1. Two types of power loss may occur: 1) long term(>˜1 second) and 2) short term (<˜1 second). The long term power lossmay be caused, for example, by a subject removing the Glasses 5.

In one exemplary embodiment, the Low Power Mode may be implemented tosave power for VPU 20. The Low Power Mode may be entered, for example,anytime the VPU 20 does not receive back telemetry from the Retinalstimulation system 1. Upon entry to the Low Power Mode, the VPU 20 turnsoff power to the Retinal stimulation system 1. After that, andperiodically, the VPU 20 turns power back on to the Retinal stimulationsystem 1 for an amount of time just long enough for the presence of theRetinal stimulation system 1 to be recognized via its back telemetry. Ifthe Retinal stimulation system 1 is not immediately recognized, thecontroller again shuts off power to the Retinal stimulation system 1. Inthis way, the controller ‘polls’ for the passive Retinal stimulationsystem 1 and a significant reduction in power used is seen when theRetinal stimulation system 1 is too far away from its controller device.FIG. 13 b depicts an exemplary block diagram 900 of the steps taken whenthe VPU 20 does not receive back telemetry from the Retinal stimulationsystem 1. If the VPU 20 receives back telemetry from the Retinalstimulation system 1 (output “YES” of step 901), the Retinal stimulationsystem 1 may be provided with power and data (step 906). If the VPU 20does not receive back telemetry from the Retinal stimulation system 1(output “NO” of step 901), the power to the Retinal stimulation system 1may be turned off. After some amount of time, power to the Retinalstimulation system 1 may be turned on again for enough time to determineif the Retinal stimulation system 1 is again transmitting back telemetry(step 903). If the Retinal stimulation system 1 is again transmittingback telemetry (step 904), the Retinal stimulation system 1 is providedwith power and data (step 906). If the Retinal stimulation system 1 isnot transmitting back telemetry (step 904), the power to the Retinalstimulation system 1 may again be turned off for a predetermined amountof time (step 905) and the process may be repeated until the Retinalstimulation system 1 is again transmitting back telemetry.

In another exemplary embodiment, the Low Power Mode may be enteredwhenever the subject is not wearing the Glasses 5. In one example, theGlasses 5 may contain a capacitive touch sensor (not shown) to providethe VPU 20 digital information regarding whether or not the Glasses 5are being worn by the subject. In this example, the Low Power Mode maybe entered whenever the capacitive touch sensor detects that the subjectis not wearing the Glasses 5. That is, if the subject removes theGlasses 5, the VPU 20 will shut off power to the external coil 14. Assoon as the Glasses 5 are put back on, the VPU 20 will resume poweringthe external coil 14. FIG. 13 c depicts an exemplary block diagram 910of the steps taken when the capacitive touch sensor detects that thesubject is not wearing the Glasses 5. If the subject is wearing Glasses5 (step 911), the Retinal stimulation system 1 is provided with powerand data (step 913). If the subject is not wearing Glasses 5 (step 911),the power to the Retinal stimulation system 1 is turned off (step 912)and the process is repeated until the subject is wearing Glasses 5.

One exemplary embodiment of the VPU 20 is shown in FIG. 14. The VPU 20may comprise: a Power Supply, a Distribution and Monitoring Circuit(PSDM) 1105, a Reset Circuit 1010, a System Main Clock (SMC) source (notshown), a Video Preprocessor Clock (VPC) source (not shown), a DigitalSignal Processor (DSP) 1020, Video Preprocessor Data Interface 1025, aVideo Preprocessor 1075, an I²C Protocol Controller 1030, a ComplexProgrammable Logic device (CPLD) (not shown), a Forward TelemetryController (FTC) 1035, a Back Telemetry Controller (BTC) 1040,Input/Output Ports 1045, Memory Devices like a Parallel Flash Memory(PFM) 1050 and a Serial Flash Memory (SFM) 1055, a Real Time Clock 1060,an RF Voltage and Current Monitoring Circuit (VIMC) (not shown), aspeaker and/or a buzzer, an RF receiver 1065, and an RF transmitter1070.

The Power Supply, Distribution and Monitoring Circuit (PSDM) 1005 mayregulate a variable battery voltage to several stable voltages thatapply to components of the VPU 20. The Power Supply, Distribution andMonitoring Circuit (PSDM) 1005 may also provide low battery monitoringand depleted battery system cutoff. The Reset Circuit 1010 may havereset inputs 1011 that are able to invoke system level rest. Forexample, the reset inputs 1011 may be from a manual push-button reset, awatchdog timer expiration, and/or firmware based shutdown. The SystemMain Clock (SMC) source is a clock source for DSP 1020 and CPLD. TheVideo Preprocessor Clock (VPC) source is a clock source for the VideoProcessor. The DSP 1020 may act as the central processing unit of theVPU 20. The DSP 1020 may communicate with the rest of the components ofthe VPU 20 through parallel and serial interfaces. The Video Processor1075 may convert the NTSC signal from the camera 12 into a down-scaledresolution digital image format. The Video Processor 1075 may comprise avideo decoder (not shown) for converting the NTSC signal intohigh-resolution digitized image and a video scaler (not shown) forscaling down the high-resolution digitized image from the video decoderto an intermediate digitized image resolution. The video decoder may becomposed of an Analog Input Processing, Chrominance and LuminanceProcessing and Brightness Contrast and Saturation (BSC) Controlcircuits. The video scaler may be composed of Acquisition control,Pre-scaler, BSC-control, Line Buffer and Output Interface. The I²CProtocol Controller 1030 may serve as a link between the DSP 1020 andthe I²C bus. The I²C Protocol Controller 1030 may be able to convert theparallel bus interface of the DSP 1020 to the I²C protocol bus or viseversa. The I²C Protocol Controller 1030 may also be connected to theVideo Processor 1075 and the Real Time Clock 1060. The VPDI 1025 maycontain a tri-state machine to shift video data from Video Preprocessor1075 to the DSP 1020. The Forward Telemetry Controller (FTC) 1035 packs1024 bits of forward telemetry data into a forward telemetry frame. TheFTC 1035 retrieves the forward telemetry data from the DSP 1020 andconverts the data from logic level to biphase marked data. The BackTelemetry Controller (BTC) 1040 retrieves the biphase marked data fromthe RF receiver 1065, decodes it, and generates the BFSR and BCLKR forthe DSP 1020. The Input/Output Ports 1045 provide expanded IO functionsto access the CPLD on-chip and off-chip devices. The Parallel FlashMemory (PFM) 1050 may be used to store executable code and the SerialFlash Memory (SFM) 1055 may provide Serial Port Interface (SPI) for datastorage. The VIMC may be used to sample and monitor RF transmitter 1070current and voltage in order to monitor the integrity status of theretinal stimulation system 1.

Accordingly, what has been shown is an improved visual prosthesis and animproved method for limiting power consumption in a visual prosthesis.While the invention has been described by means of specific embodimentsand applications thereof, it is understood that numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is therefore tobe understood that within the scope of the claims, the invention may bepracticed otherwise than as specifically described herein.

1. A visual prosthesis apparatus comprising: a camera for capturing avideo image; and a video processing unit associated with the camera andassociated with a retinal stimulation system, wherein the videoprocessing unit is configured to convert the video image to stimulationpatterns and transmit the stimulation patterns to the retinalstimulation system for stimulation of neural tissue in a subject's eye,and the video processing unit is configured to stop transmitting thestimulation patterns to the retinal stimulation system when the retinalstimulation system does not transmit back telemetry or when the retinalstimulation system detects an error in a forward telemetry received fromthe video processing unit.
 2. The visual prosthesis apparatus of claim1, wherein the retinal stimulation system is configured to notify thevideo processing unit of the error.
 3. The visual prosthesis apparatusof claim 2, wherein the retinal stimulation system is configured to stopstimulating neural tissue in the subject's eye until the error isresolved.
 4. The visual prosthesis apparatus of claim 2, wherein thevideo processing unit is configured to limit power transmitted to theretinal stimulation system.
 5. A method for limiting power consumptionin a visual prosthesis apparatus comprising a retinal stimulation systemand a video processing unit, the method comprising: a) transmittingpower and data via forward telemetry to the retinal stimulation system;b) determining if the retinal stimulation system is transmitting a backtelemetry to the video processing unit; c) stop transmitting the powerand the data via forward telemetry to the retinal stimulation systemwhen the retinal stimulation system does not transmit the backtelemetry; d) transmitting the power to the retinal stimulation systemfor a predetermined amount of time; e) determining if the retinalstimulation system is transmitting the back telemetry during thepredetermined amount of time; f) stop transmitting power to the retinalstimulation system when the retinal stimulation system does not transmitthe back telemetry during the predetermined amount of time; and g)repeating features d) through f) until the retinal stimulation systemtransmits the back telemetry.